试述润滑的作用?
参考答案:
机械的磨擦力减少到最低限度,保持原动力;机械的磨耗减少到最低限度,不但能保持正确的机械运动,而且能减少机械检修费和运用费并能延长机械使用寿命。
电梯在紧急状态下紧急电动操作特点正确的是()。
A.紧急电动运行时,安全开关仍有效
B.操作紧急电动运行开关时,操作者应能直接观察到电梯驱动的主机
C.紧急电动运行的速度不应大于0.63m/s
D.紧急电动运行开关应是须持续揿按的点动按钮
He is now _____, so he has to look for a job in a short time. Otherwise, his family will face the trouble of
lacking money. [ ]
A. at work
B. out of work
C. for work
D. on the way to work